Christeen Barbado, 52, of North Providence, says she was walking her dog, Bailey, in Lincoln Woods State Park when the shooting occurred.

LINCOLN — A Massachusetts man with a violent past was shot in the face when he tussled with an undercover state police detective during a sting at Lincoln Woods State Park early Friday afternoon, the state police said.

Col. Brendan P. Doherty said that Arjusz Roszkowski, 26, of North Reading, was planning to rob a bank, so he arranged to buy a 12-gauge shotgun and a 9mm Glock from a man he believed was also a criminal.

It turned out that the seller was Christopher Zarrella, an undercover state police detective posing as a criminal who had arranged to meet Roszkowski at the park.

As more than a dozen members of the state police intelligence and tactical units waited in the woods 15 to 20 feet away, Roszkowski showed Zarrella money for the guns, Doherty said.

Zarrella identified himself as a state police detective. Doherty said that Roszkowski reached into his waistband and pulled out a loaded 9mm handgun.

Doherty said Zarrella tackled the man and they wrestled for control of the gun. The gun fired, he said, shooting Roszkowski in the chin. The bullet ripped through his throat and exited out of his ear.

Roszkowski was taken to Rhode Island Hospital, where, according to Attorney General Patrick C. Lynch, he has a “50-50” chance of survival, Doherty said. Zarrella had powder burns on his hands and minor injuries to one of his arms.

Doherty appeared at a news conference in a parking lot off of Route 295 in Cumberland about three hours after the 12:30 p.m. shooting in Lincoln. He said he was relieved that Zarrella had escaped a very close brush with death.

“[Roszkowski] was taking the gun out of his waistband to shoot a trooper,” he said. “This gentleman came ready for business.”

Doherty said the police took no chances with Roszkowski, who has served time in prison in New Hampshire for robbery and larceny. Doherty said the undercover operation began this week and the arrangement for the gun sale was made. Yesterday morning, troopers trailed Roszkowski from Massachusetts to the meeting spot in Lincoln Woods.

State police Lt. Raymond B. Studley, of the intelligence unit, said about 15 troopers were positioned in the woods about 15 feet from where Roszkowski met Zarrella. The police also secured the site before the meeting to make sure that no passers-by were in danger.

The hilly, 2.5-mile loop around Olney Pond is a popular running spot for Providence College and high school cross-country teams. At lunchtime, many workers in the Blackstone Valley jog or walk the loop, named after Les Pawson, of Pawtucket, a three-time winner of the Boston Marathon.

By 1:30 p.m., some of the state troopers who had descended on the park were seen leaving the park’s entrance off Twin River Road. Forty-five minutes earlier, leaders in the department — including the second in command — were driving to the scene, according to Lt. James Demers, the department’s assistant detective commander.

A college residence hall director at Providence College, Arthur Dylag, 28, said he was running the loop when he noticed a couple of black SUVs.

At least five men in army fatigues, armed with rifles, emerged from one of the SUVs yelling and screaming, Dylag said. He said he could not see whom the men were yelling at. He continued to run, and within a minute, he heard what sounded like a firecracker but might have been a gunshot.

“It looked like a [Reserve Officers’ Training Corps] drill,” said Dylag, who recalled seeing similar ROTC training exercises at PC.

At Lincoln Woods, shortly before 1 p.m., a North Providence resident described police SWAT-team activity that she had witnessed. Christeen Barbado, 52, said she was walking her dog, Bailey, along a road in the park when she saw what she described as a police SWAT team running toward an area in a parking lot with their rifles.

Barbado said that after noticing the officers, she saw a body on the ground. She spoke with a man in the area who told her he had heard a gunshot, she said.

mreynold@projo.com